Anchoring the Torsion Potential of Biphenyl at the Ab Initio Level: the Role of Basis Set versus Correlation Effects

The torsional profile of biphenyl has been calculated by means of quantum-chemical perturbations and coupled-cluster methods of increasing accuracy. The performance of the various theoretical approaches has been assessed through a critical comparison with experimental barrier heights. The theoretical data indicate that the basis set effects become more critical than the correlation effects beyond the perturbational MP4 or variational CCSD(T) levels of theory to obtain the most accurate results. We also discuss the various additional corrections that would be required beyond the scope of our study to provide the best match to the experimental results.